Reason 2 is the reflexive property. Which basically says "any segment is congruent to itself"
Reason 3 is SSS (side side side) congruence theorem. The first two pair of sides are provided in statement 1 (given) and the third pair of sides is from statement 2
Reason 4 is CPCTC which stands for: corresponding sides of congruent triangles are congruent. In short, if two triangles are congruent, then the corresponding pieces are. In this case, angle N corresponds to angle P. So because the triangles MPO and MNO are congruent, then angle N = angle P. Notice how angle N and angle P are the middle letter of the two sequences MPO and MNO